1. Field of the Invention
The present invention relates an image recording apparatus and method, and more particularly to an image recording technique suitable for concealing print nonuniformity (streak error) in the form of streaks in the sub-scanning direction in an inkjet recording apparatus equipped with a full-line recording head having a row of nozzles that corresponds to the entire recordable width along the main scanning direction.
2. Description of the Related Art
In an inkjet recording apparatus provided with a line head with a row of nozzles that covers the entire width of the recording paper, recording is normally carried out with just a single nozzle for the same position in the main scanning direction (nozzle array direction), so that variation in the dot size and position due to the variable performance of a nozzle appears as a streak in the sub-scanning direction (paper conveyance direction).
Japanese Patent Application Publication No. 10-157135 discloses that streak error is inhibited with a configuration in which a plurality of nozzles are disposed in the same position in the main scanning direction, the nozzle to be used for recording is selected from the plurality of nozzles to eject droplets, and droplet ejection from the same nozzle in the sub-scanning direction is not continued for a large number of ejections. However, this configuration requires that two or more rows of nozzles be disposed in the sub-scanning direction, and there is a drawback in that the number of nozzles increases.
Japanese Patent Application Publication No. 2000-326497 discloses a method whereby streaks are rendered unnoticeable by randomly or periodically varying dot sizes produced by the ejection of droplets from the same nozzle. However, in this method, the dot sizes must be changed when ejecting droplets, and varying the dot sizes increases the complexity of the drive control (control for each nozzle) for the inkjet head. Also proposed in Japanese Patent Application Publication No. 2000-326497 is the concept of varying the dot sizes, but no specific mention is made as to the manner in which the variation is to occur and under what conditions, and there is no disclosure as to the relationship between the dot size, nozzle spacing (nozzle pitch) in the main scanning direction, droplet ejection density in the sub-scanning direction, and various other conditions.
As the demand for higher resolution and quality has increase in recent years, development of high density recording is being advanced whereby the nozzle pitch is decreased and the droplet ejection spacing is reduced in the sub-scanning direction, but when images are recorded with such high density, the degree of freedom in dot arrangement is increased while the effect of dots produced by the droplet ejection from nearby nozzles also increases. Japanese Patent Application Publication No. 2000-326497 does not provide consideration for this point, and it is difficult to refer to this method as an optimal control method for inhibiting nonuniformity.